1. Field of the Invention
The present invention relates to a driver device for driving a capacitive light emitting element.
2. Description of the Related Art
At present, display panels composed of capacitive light emitting elements are called capacitive display panels and marketed as wall-mounted TVs. Typical wall-mounted TVs are plasma display panels (hereinafter called ‘PDP’) and electroluminescence display panels (hereinafter called ‘ELDP’).
FIG. 1 of the attached drawings shows part of a driver device that causes a capacitive display panel to emit light by applying a variety of drive pulses to the capacitive display panel. This driver device is disclosed in Japanese Patent Kokai (Laid-Open Application) No. 2002-156941.
As shown in FIG. 1, a PDP 10 includes a plurality of row electrodes (not shown) and a plurality of column electrodes Z1 to Zm arranged to intersect one another. Discharge cells (not shown), which correspond with pixels, are formed the points of intersection between the row and column electrodes.
A column electrode driver circuit 20 includes a power supply circuit 21, which generates a resonance pulse supply voltage in accordance with switching signals SW1 to SW3, and a pixel data pulse generation circuit 22, which generates pixel data pulses that are to be applied to the column electrodes Z1 to Zm on the basis of the resonance pulse supply voltage. The pixel data pulse generation circuit 22 includes switching elements SWZ1 to SWZm and SWZ10 to SWZm0, which are each turned on and off individually in accordance with one display line's worth (m) of pixel data bits DB1 to DBm that designate the state (lit or unlit) of the respective discharge cells. Each of the switching elements SWZ1 to SWZm is turned on (enters the ON state) when the pixel data bit DB supplied thereto is logic level 1, for example, and applies the resonance pulse supply voltage of the supply line 2 to the corresponding column electrode Zi (Z1 to Zm) On the other hand, when the pixel data bit DB is logic level 0, the switching element SWZi0 (SWZ10 to SWZm0) enters the ON state and applies the ground potential to the column electrode Zi. That is, when a resonance pulse supply voltage is applied to the column electrode Zi, a high-voltage pixel data pulse is generated and supplied to the column electrode Zi, whereas, when the ground potential is applied to the column electrode Zi, a low-voltage pixel data pulse is generated and supplied to the column electrode Zi.
The operation of the power supply circuit 21 for generating this resonance pulse supply voltage will be described below.
Switching signals SW1 to SW3, which repeatedly set the corresponding switching elements S1 to S3 to the ON state in the order of the switching elements S1, S3, and then S2, are supplied to the switching elements S1 to S3 in order to operate the power supply circuit 21.
When only the switching element S1 enters the ON state in response to the switching signal SW1, the capacitor C1 is discharged and the discharge current thereof flows to the power supply line 2 via the coil L1 and diode D1. If, at this time, the switching element SWZi of the pixel data pulse generation circuit 22 is in the ON state, the discharge current flows into the column electrode Zi of the PDP 10 via the switching element SWZi, the load capacitor C0 that is parasitic on the column electrode Zi is charged, and an accumulation of electrical charge occurs within the load capacitor C0. In the meantime, the potential of the power supply line 2 gradually rises because of the resonance action caused by the coil L1 and the load capacitor C0. This increase of the voltage is the rising edge of the above-mentioned high-voltage pixel data pulse.
When the switching element S3 alone enters the ON state in response to the switching signal SW3, a power supply voltage Va generated by a DC power supply B1 is applied to the power supply line 2. The power supply voltage Va is the maximum voltage of the high-voltage pixel data pulse.
When the switching element S2 is alone turned on in response to the switching signal SW2, the load capacitor C0 that is parasitic on the column electrode Zi of the PDP 10 is discharged. This discharge current flows into the capacitor C1 via the column electrode Zi, the switching element SWZi, the power supply line 2, the coil L2, the diode D2, and the switching element S2, whereby the capacitor C1 is charged. That is, the electrical charge that has accumulated in the load capacitor C0 of the PDP 10 is recovered by the capacitor C1 provided in the power supply circuit 21. The voltage of the power supply line 2 gradually drops in accordance with the time constant that is determined by the coil L2 and load capacitor C0. This voltage drop is the trailing edge of the high-voltage pixel data pulse.
As a result of the above described series of operations, a resonance pulse supply voltage having gradual voltage variation in the rising and trailing edges is generated and supplied to the pixel data pulse generation circuit 22 via the power supply line 2. When the switching element SWZi enters the ON state in accordance with the pixel data bit DB of logic level 1, the resonance pulse supply voltage itself is applied to the column electrode Zi as the high-voltage pixel data pulse.
Therefore, the column electrode driver circuit 20 recovers electrical charge that has accumulated in the PDP 10, which functions as a capacitive load, and uses the recovered electrical charge when the rising edge of the pixel data pulse is generated. This reduces electrical power consumption.
Of the pixel data pulse generation circuit 22 and power supply circuit 21 in the column electrode driver circuit 20, the pixel data pulse generation circuit 22 is constructed by means of a single IC chip. On the other hand, the power supply circuit 21 includes the switching elements S1 to S3, the capacitor C1, the diodes D1 and D2, and the coils L1 and L2, and each of these components needs a relatively large current. Thus, each of the components of the power supply circuit 21 is a discrete component. It is therefore necessary to place eight discrete components that correspond to the switching elements S1 to S3, the capacitor C1, the diodes D1 and D2, and the coils L1 and L2 near the IC chip of the pixel data pulse generation circuit 22. Accordingly, the electric power consumption and the mounting area of the components are large.